The present invention relates to a charging system for charging an electric vehicle by use of electromagnetic induction and, in particular, to an improved coil cooling structure.
A charging system of this type is able to supply power to an electric vehicle with no intervention of an electric contact, that is, in a non-contact manner. Due to this, the charging system of this type provides various advantages and there have been proposed various structures for such charging system. Referring to the basic structure of the charging system, for example, as disclosed in Unexamined Japanese Patent Publication 5-258962, 5-260671, 6-14470 and the like, there is applied the principle of a transformer that coils are respectively wound around primary and secondary cores and, when charging the electric vehicle, an alternating current is allowed to flow through the primary coil to thereby cause the secondary coil to generate an electromotive force due to electromagnetic coupling.
The charging system of this type is strongly required to be compact as a whole and, in order to attain such compact charging system, it is necessary to cool the coils sufficiently during the charging operation of the electric vehicle. As described above, the basic principle of the present charging system is derived from the transformer and thus, as the cooling structure of the charging system, there is applied a similar structure to the transformer; for example, in U.S. Pat. No. 5,412,304, as shown in FIGS. 31 and 32, there is employed a structure in which a core 2 is stored in a housing 1, a primary coil 3 is wound around the outer periphery of the core 2, and there are formed a large number of cool air passages 4 extending along the primary coil 3 as well as air exhaust ports 5 in communication with the cool air passage 4. And, a cool air supply hose 6 coming from a cooling device is connected to the housing 1 so that the open air can be supplied into the cool air passages 4, that is, if the open air flows through the cool air passages 4 and flows out from the air exhaust ports 5, then the heat of a primary coil unit as well as the heat of a secondary coil unit disposed adjacent to the primary coil unit can be discharged.
However, in the above-mentioned structure, the heat generated in the primary coil 3 is cooled only from the outside thereof and thus the cooling efficiency of the primary coil 3 cannot be enhanced to a sufficient degree, so that the heat is easy to remain in the interior portion of the primary coil 3. Also, since heat is generated not only in the primary coil 3 but also in the core 2, in order to cool the heat of the core 2, as shown in FIG. 32, it is necessary to provide a refrigerant passage 4 in the neighborhood of the core 2. Further, for the sake of efficient cooling of the primary coil 3, there are arranged a large number of refrigerant passages 4 extending along the primary coil 3, which is unable to enhance the rate of occupation of the primary coil 3 but increases the size of the whole charging system.
Also, in the above-mentioned structure, there is found a further problem: that is, because the open air is simply supplied to the neighborhood of the heat generated portions of the structure, the cooling efficiency is still not sufficiently high and the heat is easy to remain in the interior portion of a charging coupler.
Further, in the above-mentioned structure, there is found a still further problem: that is, in order to remove the heat within the coil unit, it is necessary to provide a special cooling device.